Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that has a function to clean the exhaust air from the inside of the apparatus and discharges the cleaned air.
Description of Related Art
The exhaust air from an electrophotographic image forming apparatus generally contains harmful matters, such as volatile organic components (VOC), ultrafine particulates (UFP), etc. In an image forming apparatus as disclosed in Japanese Patent Laid-Open Publication No. 2006-215307, a filter serving to trap these harmful matters is provided in an exhaust air duct leading the air inside the apparatus to the outside. In a conventional image forming apparatus of this type, an exhaust fan is also provided, which affects the efficiency of trapping harmful matters in the filter. In the conventional image forming apparatus, when lots of harmful matters are generated, the rotation speed of the exhaust fan is lowered so as to improve the efficiency of trapping harmful matters in the filter.
Lowering the rotation speed of the exhaust fan so as to improve the efficiency of trapping harmful matters in the filter is based on a thought that there is a correlation between the efficiency of trapping harmful matters in a filter and the flow rate of the harmful matters coming into the filter. Specifically, it is considered that the lower the flow rate of harmful matters coming into the filter, that is, the lower the rotation speed of the exhaust fan, the higher the efficiency of trapping the harmful matters in the filter. However, lowering the flow rate of harmful matters coming into the filter creates a risk of leaking the harmful matters from the vicinity of a fixing unit.